Automatic propeller feathering system



July 1, 1952 R. A. MUMA AUTOMATIC PROPELLER FEATHERING'SYSTEM Filed May 10, 1949 .NS h

INVENTOR. /Wfwo r9. /fa/v RWM Patented July l, 1952 UNITED STATES rem OFFICE AUTOMATIC PROPELLER FEATHERING STEM Richard A. Muma, Wichita, Kans.,

assigner to Beech Aircraft Corporation, Wichita, Kans., a

corporation of Delaware Application May 10, 1949, vSerial No. 92,355

s claims. (c1. 17o- 13529) tion of the feathering of the propeller of that engine and t prevent unfeathering operations until so intended by the pilot.

Particularly it is a ,purpose of the invention to simplify and reduce the number of circuits and parts required.

Further special objects of the invention are to provide the pilot with suitable indication when the system is properly armed and to be relied upon, to give the pilot absolute control at al1 times for use or non-use of the system and to provide for complete preiiight checking of the system.

Other desirable objects attained .by the invention are set forth or .willappear in the course of the following specification.

The drawing accompanying and forming part of the specification is a diagrammatic illustration of a present preferred embodimentof the invention. `Structure and arrangement, however, may be variously modied and changed as regards the immediate illustration, all within thetrue intent and broad scope of the invention as hereinafter dened and claimed. Y y

The single gure in the drawing is a wiring diagram showing how the various units which go to make up the system may be combined to effect the desired results outlined.'v

The present system is like that disclosed in the patent application above-identiiied as involving certain safety or precautionary circuits arranged to exercise supervisory control over the normal feathering circuits as represented by the normal feathering switches I and .normal feathering relays 2 for each engine.

Thus there is provided at each enginea torque switch 3 for sensing loss of power and a range switch 4 conditioned by throttleV and mixture levers 5 and 6 to arm the circuit for the torque switch at a time when maximum power for takeoir is required.

Also, there is provided a timer 'Infor permitting initiation of the feathering cycle only if power is absent for a denite limited period of time Such as for an intervaloi one second anda lockin relay 8 for maintaining circuits closed once the feathering cycle has been initiated.

Under the present invention, however, only a single timer and only one lockin relay are required. y

This is made possible by theV provision of an engine selector relay 9 designed to cut the timer and the lookin relay in on the power failingy engine detected and/ ,identied Vby a particular torque switch.

The torque switches 3, of either the mechanical or pressure type, are shown connected atIE with a battery or other power source VII vand operate each to close in the the engine. Y

Signal lights I2 suitably placed on the .engine panel or elsewhere are connected at I3 to indij.

cate which, if any engine, is lacking in torque.

Each torque switch is connected by a line I4V with the range switch 4 for that engine and these range switches are separately connected by lines I5, `lli with magnet windings Il, VI8 of the engine selector relay 9 so that closing of either torque switch in the two-engine installation illustrated, with throttle in the full power position and mixture lever set at automatic rich, one or the other of magnet coils Il, l8 will be energizedv The timer 'i is shownas of the electronic type, connected at one side. at IS y I6, andat the opposite side at 2Q with circuit closers 2l, 22 operated respectively by magnets I'I and I8 of the engine selector relayv S.

Thus, with operation of the torque switch designated for the left hand engine and consequent energization of magnet. I'I, vcircuit will be closed at2I throughline 23 leading to magnet 24 of the lookin relay 8 and with energization of magnet I8 for the right hand engine, circuit will be closed at 22 through line 25 to the right hand engine magnet 26 of lookin relay 8.

` TheV delayed action timer 1 prevents the lookinV relay from functioning until-the torque'switch has been closed fora full second or for such other interval of .time for which it has been designed.

At the end of the predetermined interval of time, the magnet 24 or 26 of the lookin relay I3 will be energized to close the circuit (magnet 24) through connections 23, 21, armatures 28, 2S and line 3l) through the normal feathering relay 2 for the left hand engine, or through lines 25, 3l, armatures 32, 33 and line 34 `to the normal feathering relay 2 for the right handengine.

Circuits also will be completed at the same time by thelockin relay 8, in the case of the left absence 'of torque on with the power line hand engine coil 24, through line 35, armature 36, line 31, armature 38 of lockout relay 38 and line 48 to the normal feathering pressure cutout switch 4I; and in the case of right hand engine magnet 26, through connection 42, armature 43, conductor 44 to the second armature 45 of lockout relay and then by way of connection 46 to the normal feathering pressure cutout switch 41. In each instance the selected magnet 24 or 26 of the lockin relay 8 has a sustaining circuit through the normal feathering `pressure cutout switch for that particular engine, which remains closed, supplying power to the normal feathering relay 2 until the feathering cycle is completed, regardless of whether the torque switch continues closed during this feathering period.

This automatic safety feathering can be accomplished in short order, for example, in a total` elapsed time of six seconds from moment of loss of torque.

Further, this automatic feathering is operative only in the full power range of the engine, say from approximately three-quarters to full throttle, as determined by the range switch jointly controlled by the throttle and mixture levers covering range of full power throttle settings from sea level to critical altitude for engine over boost. y

The delayed action of the timer prevents the automatic circuit from functioning until the through operation b-y the pilot of the proper one of the normal feathering switches I or by manual operation of a special reset switch indicated at 55 and arranged to close a connection at 55 from the power line I0 through conductor 51 to the reset coil 58 of relay 39.

The automatic resetting is accomplished in the example when the upper or right hand engine feathering switch I is operated, by passage of current across contacts at 59 and through conductor 69, the normally closed back contacts 6I of reset switch 55, armature 62 of reset relay 63 and conductor 51 to reset coil 58. In the case ofthe lower or left hand normal featherng switch I, the connection of contacts at 64 establishes a circuit through line 65 to reset relay 63 which thereupon shifts armature 62 to contact torque switch has been closed for a full second or other predetermined period so as not to operate on a momentary loss of power and requiring for operation, a full second of loss, or of torque less than that normally developed in the full power range.

The timer further will not activate the automatic circuit even though the torque switch has been closed for several seconds unless the throttle has been advanced past the three-quarter open position and the mixture control is in the automatic rich position, and then not until a full second after both conditions have been met.

The engine selector relay 9 automatically selects the eathering circuit for the power losing engine, as detected by the torque switch of that particular engine and shown by the engine identifying torque light I2. This relay closes only that one particular feathering circuit and thus makes it impossible to feather more than the propeller of that one non or malfunctioning engine.`

The normal feathering pressure cutout switch 4I or 41 opens when full feathered position of` the propeller of that circuit is reached. This deenergizes the holding magnet 24 or 25 of the lookin relay 8 to close a circuit of the armature 48 or 49, ,enabling condenser 59 to discharge through line 5I and armature 48 or 49 and line 52 through the lockout coil 53 of mechanical lockout relay 39 releasing the mechanical lock on armatures 38 and 45 thereby rendering all automatic circuits inoperative. l

The charging of the condenser 50 for the above purpose is eiected in the illustration during the feathering cycle through connections I9, 54, armature 48 or 49 and connection 5I.

When lockout relay 39 is activated as described by the opening of the circuit by the normal feathering cutout switch 4| or the feathering cycle, all automatic feathering circuits are rendered inoperative and will remain so until the lockout relay is reset.

The lockout relay 39 is reset automatically in.

the illustration when the propeller is unfeathered 41 at the end of 66 to run current through line 51 to the reset coil 58.

The automatic feathering circuit lockout relay 39 is mechanically locked closed when the automatic feathering circuit is operative and this eliminates any need for resetting the same each time the aircraft is used.

A reset signal light is shown at 51 connected with the power source through lines I9, 68 and having a contact 69 for engagement by armature 38 when the reset magnet 58 is energized, circuit then being completed through the ground line 48 and normal feathering pressure cutout switch. This reset light thus indicates when the lockout relay is open to ground on the automatic feathering circuit.

To enable the automatic feathering circuits to be tested for each engine prior to takeoff, there is provided in the illustration, a test switch 19, 1I for each engine, connected at 12, 13 to bypass the range switches 4 of the engines. These switches, in conjunction with the single reset switch 55 and reset signal 61, enable the pilot to fully check and put the automatic feathering circuits in condition for operation.

In these tests the pilot may energize an automatic feathering circuit when an engine is running at low torque and stop at will, allowing the engine oil pressure to then unfeather the propeller.

In order that the pilot may have absolute control at all times there is provided in the illustration a master switch 14 in the power line I0, enabling the pilot to instantly stop automatic feathering on an engine resuming power and whereupon it will unfeather the propeller by engine oil pressure. The circuit lockout relay 39 must then be reset by reset switch 55 to restore the automatic feathering circuit. Also, if the propeller blades are moved from the feathered to an unfeathered position by hand, after being feathered by the automatic circuit, the automatic circuit lockout relay must be reset by means lof the reset switch 55 or the normal feathering switch I.

The master switch 14 ordinarily may be closedv with throttles in full power position and mixturel set at automatic lean.

Servomotors for actuating trim tabs and corv` yrecting throttle settings to ltrim the airplane The system is of compact, simple design, readily applicable to existing aircraft and provides automatic safety control, in addition to absolute orarbitrary control by the pilot. l I

The test switch circuits enable the lpilot to make certain that the automatic safety circuits are-in operative condition, ready for iiight, and this together with the absolute control afforded by the master switch 14, provides a sense of security and reliability, enabling the pilot to use the system with confidence and to the fullest possible safety advantages.

Operation For normal takeoff the feathering master switch 14 is closed, as indicated in dotted lines. This arms the entire feathering system, both normal and automatic.

When ready for takeoii" the mixture control levers 6 are placed in auto-rich position and throttle levers advanced to full power range, closing range switches 4, as shown by the dotted lines.

Assuming failure of the right-hand engine during takeoi under full power range, the condition of parts will be as indicated in the broken lines, as follows:

The right-hand engine torque switch 3 closes, energizing coil I 8 of selector relay 9 through connection I4, the right-hand range switch 4, wire I6, coil I8, wire 8I and to ground by armature 82 of the deenergized selector relay coil I1.

Coil I8 closes a circuit at armature 83 from the power line I8 through connection 84 to the timer 1.

Coil I8 also closes circuit between the timer relay 85 and magnet coil 26 of lock-in relay 6, by way of conductor 20, armature 22 andl conductor 25. At such time also armature 86 of coil I 9 opens the ground circuit for coil I1 of this relay.

If the right-hand torque switch remains closed for the preselected length of time determined by timer 1, say approximately one second, the timer relay 85 will close circuit from the battery to lock-in relay coil 26 through line I9, timer relay 85, line 29, armature 22, line 25, coil 26 and to ground through line 42, armature 43 of deenergized lock-in relay coil 24, line 44, armature 45 of lock-out relay 39 and by way of line 46 through the closed contacts 81 of right-hand test switch 1I to right-hand engine normal feathering pressure switch 41.

The energized coil 26 of lock-in relay 8 connects power line I0 to condenser 58 through connections I 9, 54, armature 49 and connection 5I.

At the same time servomotor 16 is energized through lines I9, 54, armature 33, contact 80 and line 16.

The normal feathering relay 2 for the right-V hand engine is energized at this time through 55, because the lock-out lines I9, 54, armature 33 and line 34 to close the right-hand feathering motor switch 88, initiating propeller feathering operation.

The lock-in relay coil 26 also disconnects the grounding connection for the other relay coil 24, at armature 36, thus preventing coil 24 from being energized during such operations.

Coil 26 of lock-in relay 8 becomes self-energized by closing of armature 32, which then completes circuit from lines I9, 54, through lines 3I and 25 to coil 26 and to ground through the normal feathering pressure switch 41 through connections 42, 43, 44, 45 and 46.

With coil 26 self-energized as described, circuits are held closed until vthe feathering cycleA is completed. When the propeller becomes fully feathered the normal feathering pressure switch 41 disconnects the circuit to ground and coil 26 is deenergized, opening circuits at armatures 49, 33, 32, and closing grounding circuit at armature 36 for the other coil 2.4.

With the battery or power circuit broken as described, condenser 50 which has `been charged during the feathering cycle, discharges through line 5I, armature 46 of coil 24 and line 52 through trip coil 53 of the lock-out relay'f39, releasing and opening armatures 45 'and 38 of the lock-out relay, disconnecting circuit 46 to right-hand normal feathering pressure cutout switch 41 and connecting the reset lightV 61 in circuit.

Further feathering is then vimpossible until the system is rearmed through the reset switch relay 39 controls both right-hand and left-hand engine feathering systems. Reset switch 55 can be operated as above described to close circuit at 56, thus to energize the reset coil 58. of lock-out relay 39 through connections 51. e

The sequence of operation of the left-hand feathering system lis similar to the sequence of operation for the right-hand engine, as described.

Test switches, 16 for the left-hand engine and 1I for the right-hand engine, serve as by-passes for the respective range switches 4, enabling the pilot to test the circuits 'for either side at any time.

In the system here disclosed the mixture control and throttle levers must be operated in this particular sequence to 'arm the safety feathering circuits.4 This requirementA avoids arming the circuits unnecessarily as at times when automatic feathering would vnot be required and would not be in order.

What is claimed is:

1. An automatic safety feathering system for multi-engine aircraft having normal propeller feathering circuits for the engines and comprising torque switches subject to engine torque and means connecting said torque switches with said feathering circuits, including a timer for initiating delayed action of the feathering circuits and engine selector relay means controlled by torque switches of the individual engines for selectively connecting said timer with the feathering circuits of the diierent individualengines.

2. An automatic feathering system for multiengine aircraft comprising propeller feathering means for each engine, an automatic torque switch for each engine, a timer for instituting delayed action of said propeller feathering means and an engine selector controlled by said torque switches for selectively connecting said timer with the propeller feathering means of different individual engines.

3. vAn automatic safety feathering system for aircraft having a plurality of engines and comprising in combination with propeller feathering means and power loss sensing means for each engine, a delayed action timer and selector means controlled by the individual-engine power loss sensing means for automatically connecting said delayed action timer with the propeller feathering means of a power losing engine detected by said power loss sensing means.

4. An automatic safety propeller feathering system comprising in combination with the normal feathering systems of the individual engines of a plural engine installation, a torque switch for each engine, lookin relay means for maintaining said feathering systems operative throughout a predetermined feathering cycle, selector relay means controlled by said torque switches for automatically connecting said lookin relay means with the normal feathering system of a torque losing engine detected by one of said torque switches, a timer for delaying operation of said normal ,propeller feathering systems for a predetermined interval 'of time and means controlled by said selector relay means for connecting said timer 'with said lookin relay means.

5. An automatic safety propeller feathering system comprising in combination with the normal feathering systems of the individual engines of a plural engine installation, 'a torque switch for each engine, lookin relay means for maintaining said feathering systems operative throughout a predetermined feathering cycle, selector relay means controlled by said torque switches for automatically connecting said lockin relay means with the normal eathering system of a torque losing engine detected by one of said torque switches, a lockout relay for rendering said lockin relay inoperative at the end of the predetermined feathering cycle and a reset switch for releasing said lockout relay to restore the lookin relay means to operative condition.

6. An automatic safety propeller feathering system comprisingin combination with the normal feathering systems of the individual engines of a plural engine installation, a torque switch for each engine, lookin relay means for maintaining said 'feathering systems operative throughout a predetermined feathering cycle, selector relay means controlled by said torque switches for automatically connecting said lookin relay means with the normal feathering system of a torque losing engine detected by one of said torque switches, a lockout relay for rendering said lookin relay inoperative at the end of the predetermined feathering cycle, a reset switch for releasing said lockout relay to restore the lockin relay means to operative condition and a reset signal associated with said lockout relay.

7. An automatic safety propeller feathering system comprising in combination with the normal feathering systemsof the individual engines of a plural engine installation, a torque switch for each engine, lock-in relay means for maintaining said feathering systems operative throughout a predetermined feathering cycle, selector relay means controlled by said torque switches for automatically connecting said lockin relay means with the normal feathering system of a torque losing engine detected by one of said switches, a lock-out relay for rendering said lock-in relay means inoperative at the end of the predetermined feathering cycle and means for tripping said lock-out relay at the end of the predetermined feathering cycle.

8. An automatic safety propeller feathering system comprising in combination with the normal feathering systems of the individual engines of a plural engine installation, a torque switch for each engine, lock-in relay means for maintaining said feathering systems operative throughout a predetermined ieathering cycle, selector relay means controlled by said torque switches for automatically connecting said lockin relay means with the normal feathering system of a torque losing vengine detected by one of said switches, a lock-out relay for rendering said lock-in relay means inoperative at the end of the predetermined feathering cycle and means for tripping said lock-out relay at the end of the predetermined feathering cycle, including a condenser connected to be charged during the feathering cycle and a relay trip coil connected and arranged to be energized by discharge of said condenser at the end of the feathering cycle.

RICHARD A. MUMA.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,257,126 Rindfleisch Sept. 30, 1941 2,320,195 Rindfleisch May 25, 1943 2,339,090 McIntosh Jan. ll, 1944 2,346,007 Chillson Apr. 4, 1944 2,374,276 French Apr. 24, 1945 2,471,953 Hamilton May 31, 1949 

